Permeate tube and related methods

ABSTRACT

A novel positive traction permeate tube and fittings therefor are described for use in spirally wound membrane filtration elements for filtration and separation applications. Membrane filtration elements incorporate the novel permeate tube. Methods of making the novel positive traction permeate tube are also disclosed, as are the preferred sanitary stainless steel materials used for the sanitary tube and fittings. The novel permeate tube involves a sanitary tubing having two open ends, each with an end fitting. The end fittings engage a positive traction drive for high tension spiral winding of a membrane element spirally around the novel permeate tube. Membrane filtration elements made with the novel permeate tube are less subject to slippage and breakage during manufacture and can withstand higher pressure drops and flow rates during use without failure of the spirally wound membrane element. The positive traction permeate tube facilitates membrane replacements.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Ser. No. 11/984,381, filed Nov.16, 2007, now U.S. Pat. No. 8,070,088.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON COMPACT DISC

Not applicable.

REFERENCE TO A “MICROFICHE APPENDIX”

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to a novel positive traction permeate tube and amethod of making the novel positive traction permeate tube forutilization with spiral wound membrane elements used in pressurizedmembrane filtration, including microfiltration, ultrafiltration,nanofiltration and reverse osmosis. The invention pertains especially tonovel compositions, structures and configurations for the positivetraction permeate tube in a membrane filtration element and to devicesand procedures for spirally winding a membrane element about a substratepermeate tube of stainless steel, or other suitable materials, cut toprecise final length prior to winding and using positive traction duringwinding thus providing enhanced reliability of the finished spiral-woundmembrane element. The novel positive traction permeate tube preventssystem failure and destruction of the spiral wound membrane filtrationelement through breakage, channeling and unwinding thereof at higherfluid pressure drops and higher liquid feed flow rates associated withhigh viscosity retentates in membrane filtration processes.

2. Description of Related Art Including Information Disclosed Under 37CFR 1.97 and 1.98

In a spiral wound membrane filtration element, a permeate tube isarranged at the center of the spirally wound membrane element. Thepermeate passes through the membrane on each side of the wound membraneleaves, then along the permeate carrier inside the membrane leaves andthen through perforations in the permeate tube into the interior of thecenter of the permeate tube. It is through the center of this permeatetube that the permeate fraction can leave the membrane element. Thus thecentral tube in a spirally wound membrane filtration element is called a“permeate tube.” The permeate leaves the element via the permeate tubeand the retentate can be passed on to another membrane filtrationelement to increase further the concentration of high molecular weightcompounds in the retentate by extracting more permeate from the feedstream through a subsequent membrane element.

Further, for critical applications such as pharmaceutical and dairyoperations, the permeate tube must be free from bacteria traps. Spiralwound membrane elements, such as those used in the dairy field for theseparation of whey, are subject to a cleaning operation after periods ofuse, generally by the use of chemical cleaning solutions, such ascaustics, detergents, chlorine, or combinations thereof, and arethereafter rinsed with clean water.

There are many different configurations for membrane filtration elementsbut the vast majority of membrane filtration systems have spirally woundmembrane elements. Other configurations of membrane elements are tubularmembranes, hollow fiber membranes and flat sheet membranes. Membranefiltration elements comprising spiral wound membranes and theirconstruction are well known and are illustrated, for example, in U.S.Pat. Nos. 3,367,505, 4,033,878, and 4,792,401. A spiral wound membraneelement generally comprises one or more laminate leaf assemblies ofsemipermeable membrane sheet and optionally other materials. These leafassemblies are each arranged so that the feed liquid is carried over themembrane surface while permeate is carried through to a central permeatecollection tube. The step of spirally winding the membrane onto acentral tube is well known and demonstrated, for example, by Bray, U.S.Pat. No. 4,021,351.

Spiral wound membrane elements are a widely used membrane configurationin present day sanitary membrane filtration applications. Such membraneelements are installed inside elongated pressure vessels which maycontain one or a series of up to six membrane elements or more. A highpressure feed stream enters the vessel through its inlet port at one endof the vessel and exits through its outlet port at the opposite end. Thelinear speed and high pressure drop is substantial, thereby posing athreat to the integrity of the membranes.

In the pharmaceutical, food & beverage, and biotech industries,contamination-free processing is critical. The integrity of the sanitarymanufacturing equipment is essential for full compliance with thevalidation process. The potential for contamination increases with theintroduction of peripheral components, such as filtration andtemperature and pressure measuring instrumentation required to ensureprocess parameters remain within acceptable limits. As a result, theseinline devices must themselves meet standards set by governing agenciesto ensure there are no weak links in the sanitary chain.

The two most common of these standards include: (1) the “3A” standardpromulgated by 3A Sanitary Standards, Inc. (3A SSI), a non-profitassociation representing equipment manufacturers, processors, regulatorysanitarians and other public health professionals. 3A Sanitary Standardsand 3A Accepted Practices pertain to dairy and food processingequipment, and focus on sanitary design, materials, and surface finish;and (2) the “FDA-Approved” standard promulgated by the United StatesFood & Drug Administration (FDA), a federal agency that regulates allfood processing and drug manufacturing in the U.S. It sets and enforcesstandards and government codes.

Most spiral-wound membrane elements now manufactured are rolled over apermeate tube made of plastic material, commonly polysulfone. In theprior art, a conventional torque force is applied in winding a spiralwound membrane element around a polysulfone tube. Plastic permeate tubesused in conventional manufacturing processes are longer than the tubesfound in finished membrane elements as the original length of tube iscut to size after applying the spiral wound membrane to the substratetube. A conventional spiral wound tube membrane filtration element isshown in FIG. 1. The wound element 10 involves a plastic permeate tube11 having at least one notch 15 on one end for engaging a drive system,not shown, to wind the permeate tube 11 around which a membrane element12 is wound under a conventional tension. The prior art permeate tubesare subject to mechanical slippage and breakage while winding themembrane element. Unlike the prior art, the permeate tubes of thepresent invention do not slip or break because they provide positivetraction through an interlocking means, as will be discussed in greaterdetail in the Summary of the Invention.

The driving force required to roll the elements in a prior art permeatetube is applied to the ends of the permeate tube 11 by inserting arolling machine chuck into the notch 15 cut at the end of the tube 11 asshown in FIG. 1. The notches 15 are eliminated with the excess length ofthe membrane element 12 and the plastic permeate tube 11 when theassembly is cut to its final length as shown in FIG. 2.

The entire assembly is cut at the ends, typically using a saw or othercutting means, to allow for placement in a membrane filtration vesseland so that the ends of the cut plastic permeate tube 11 may engageother elements in filtration vessel, by means of interconnectors or ATDs(Anti Telescoping Devices). Unlike the prior art, the invention does notcut the tube to length after wrapping but instead utilizes a tube of thedesired precise length and positively wraps the membrane leaves to thefinal tube as will be discussed in greater detail in the Summary of theInvention.

For example, Bray, U.S. Pat. No. 4,021,351, teaches a membrane cartridgethat is spirally wound around an injection-molded plastic permeatecollection tube having transverse slits or tongue extensions at the end.The permeate tube can be made up of a plurality of interlocking plasticpieces mated with each other through the transverse slits or tongueextensions at the end of each tube segment. The membrane materials arethen spirally wound upon the interlocking pieces of plastic permeatetube to form a membrane element.

In membrane filtration processes involving high viscosity retentate, therequired higher fluid pressure drop and higher flow rates involved cancause channels to form between membrane layers while a filtrationelement is in use. This can occur at any time, and sometimes after onlya few seconds of use under high pressure drop and high flow rate.“Channeling” is especially prevalent in spiral wound membrane elementsfor ultrafiltration of high viscosity retentate in partially filtereddairy liquids when the membrane element is wound about the permeate tubeunder conventional winding tensions, thus causing failure in thespirally wound membrane element while in use.

To avoid this failure, higher winding tensions are required in windingthe membrane element to the permeate tube. However, when a membranefiltration application requires that the membrane element be rolledunder higher than conventional winding tension, the prior art plasticpermeate tubes tend to break, especially at the notches, thus causingunacceptable waste in the manufacturing process.

Changing only the composition of the permeate tube to stainless steel,instead of polysulfone, avoids the problem of breaking the tubes butintroduces a new problem: cutting off the ends of the membrane element,including the stainless steel permeate tube, produces elements with toobig variation of finished length as well as irregular end-faces of thetube. Cutting the stainless steel permeate tubes, of prior art design,before winding the elements leaves the tube without the slots at itsends and without positive traction. The driving force required forwinding is reduced to whatever friction is available between theinterior of the prior art stainless steel permeate tube and expandingchucks inserted at the ends of the tube and attached to the drive systemof the rolling machine. This configuration results in slippage when theelement is rolled under higher than conventional winding tension.

In conventional prior art tubes, failure due to slippage or breakageoccurs at greater frequency as the winding tension is increased.Further, in the prior art little or no attention has been given tomeasuring torque or slippage in wrapping the membrane element andnothing known has been done to provide an accurate means of controllingand measuring torque or the tightness of the spiral wrap.

A positive traction substrate permeate tube of precise length andend-faces is needed that can withstand high torque and function underprecise mechanical control that permits high tension winding in theproduction of a spiral wound membrane element without the substratepermeate tube slipping or breaking, and can withstand the pressureforces exerted on the tube while winding the membrane element and thehigh pressure drop and endure the high fluid flow conditions while inuse in a filtration element.

SUMMARY OF THE INVENTION

As previously discussed the invention provides a novel permeate tubehaving a different composition, structure and configuration than theprior art permeate tubes to provide a novel substrate for spiral woundmembrane elements for pressurized membrane filtration. The novelpermeate tube is designed for winding a membrane element around the tubeunder positive traction providing for high tension membrane winding in acontrolled, measurable and repeatable operation, to produce a permeatetube with the tightness of the membrane element controlled by vacuum,positive traction fittings and the drive bar while securing a precisefinished length of the membrane element.

The characteristics of the permeate tube of the present invention are:(a) the tube is stainless steel allowing high tension winding withpositive traction and (b) the positive traction permeate tube ismachined to precise length prior to winding of the membrane elementthere over. These characteristics (a) preserve the integrity of theelement and (b) allow the seal of the ATD to be very close to the end ofthe permeate tube, thus securing good cleaning, even with high viscosityretentates.

The novel permeate tube can undergo high tension winding of the membraneelement without any tube breakage or slippage during high tensionwinding. In addition, the novel permeate tube is prepared fromcomponents manufactured under precise size tolerances in order that thenovel permeate tube may be utilized as a finished component directly inthe manufacturing of a membrane filtration element.

Unlike the prior art, the novel positive traction permeate tubes of theinvention are not cut to size after winding the membrane element. Thecomponents of the novel positive traction permeate tube are designedwith precise tolerances as to size prior to assembly into the novelpositive traction permeate tube structure, as well as after theassembly, thereby abating any need to cut or saw the novel permeate tubeto a shorter length after the membrane element is wound around the tube.Having permeate tubes of precise finished length is essential to securethat all unions between permeate tubes and adjacent interconnectors-ATDsplace the sealing devices (O-ring, leap seal, etc) very close to the endof the permeate tube, a condition required to effectively clean theinside of the permeate tube comprised between its end and the sealingdevice. This is especially important in cases of high viscosityretentates.

It is an object of the invention to provide an interlocking means on theends of the finished tube for making spiral wound membrane elementsunder high tension winding using positive traction in which the torquein the wrapping of the spiral wound membrane leaves can be preciselycontrolled and the tightness of the spiral wrapped membrane leaves canbe controlled. It is another object of the invention to provide a novelpermeate tube that distributes the stress on the central sanitary tubingduring high tension winding without slipping or breaking. It is yetanother object of the invention to provide a novel permeate tube that isnot subject to slippage and breakage under high torque and vacuumconditions during the membrane element winding process.

It is yet another object of the invention to provide a permeate tubethat enables production of a spiral wound membrane filtration elementthat can withstand higher fluid flow rates and higher fluid pressuredrop without substantial channeling, unwinding or other failures in thespiral wound membrane element during high fluid pressure drop and highfluid flow in a membrane filtration process involving high viscosityretentate separation by providing a spiral wrapped membrane on thepermeate tube substrate with a controlled torque and wrap tightness.

A positive traction permeate tube comprises (A) a substantiallycylindrical sanitary tubing having a first open end, a second open end,a sanitary tubing wall defining a sanitary tubing interior andsubstantially circular sanitary tubing exterior, a sanitary tubinglongitudinal axis and a plurality of perforations in the sanitary tubingwall providing access to the sanitary tubing interior; (B) a firstfitting at said first open end and having a longitudinal axis, saidfirst fitting being affixed contiguous with the first open end of thesanitary tubing such that the longitudinal axis of the sanitary tubingand the longitudinal axis of the fitting are parallel and coincident,said first fitting having a longitudinal opening cut through a solidpiece of said first fitting, the longitudinal opening defined by atleast one surface against which an applied force produces a moment offorce having a vector perpendicular to and displaced from thelongitudinal axis of the sanitary tubing and the parallel and coincidentlongitudinal axis of the fitting when affixed contiguously with thefirst open end of the sanitary tubing; and (C) a second fitting at saidsecond open end and having a longitudinal axis; said second fittingbeing affixed contiguous with the second open end of the sanitary tubingsuch that the longitudinal axis of the sanitary tubing and thelongitudinal axis of the second fitting are parallel and coincident, thesecond fitting having a longitudinal opening cut through a solid portionof the second fitting, the longitudinal opening defined by at least onesurface against which an applied force produces a moment of force havinga vector perpendicular to and displaced from the longitudinal axis ofthe sanitary tubing and the parallel and coincident longitudinal axis ofthe second fitting when affixed contiguously with the second open end ofthe sanitary tubing.

Referring to the inside and outside cross-section of the permeate tube:(A) the inside cross section of the permeate tube can have any shape inthe central tubing and inside end of the fittings (the opening forpositive traction) but it must be circular on the outside ends of thefittings to allow the connection and seal with the ATDs; and (B) theoutside cross section of the permeate tube must be circular along theentire length of the permeate tube because the membrane element, woundon the permeate tube, must be substantially cylindrical to obtain atight fit inside the pressure vessel that houses the permeate tube.

In a preferred embodiment of the invention, the permeate tube iscomprised of a 316L stainless steel central tubing with fittings ateither end. The fittings are made of the same 316L stainless steelmaterial as the sanitary central tubing. The fittings are of cylindricalshape, having an outside diameter equal to the outside diameter of thecentral tubing and a length of 2 inches. The length of the fittings isnot critical. In fact the fitting affixed to either end of the centraltubing may be of different length. The length of the permeate tube isthe sum of the length of the central tube and the lengths of thefittings affixed on the ends of the central tube.

Referring to the structure of the fittings, each fitting has two ends:the interior end is adapted to be butt-welded to one of the ends of thecentral sanitary tubing; the exterior end serves as one end of thefinished permeate tube. When both fittings have been welded to theopposing ends of the central sanitary tubing the permeate tubeperforations are made and the permeate tube is ready to wrap with amembrane element. Each end of the fitting has a face defined by a planeperpendicular to the axis of the fitting. The interior end has the samedimensions as the sanitary tubing end to which it is butt-welded;including outside diameter and wall thickness.

The exterior ends of the fittings have a cylindrical opening, coaxialwith the fitting, with a thicker wall than the interior end, having inthe preferred embodiment an inside diameter of 1.318 inches for an 8″membrane element, which provides the cylindrical inner surface requiredto accept an ATD with a sealing device (O-ring, leap seal, etc.). Bothends have cylindrical openings coaxial with the fitting and bothopenings are shorter than the fitting itself. The section of the fittingbetween the openings at both ends of the fitting has an opening, alsocoaxial with the fitting. This central opening is preferably hexagonal(or any other polygonal shape) and provides the surfaces to engage adriving bar. Configurations other than polygonal configurations aresuitable for the central opening provided they are capable of achievingpositive traction by engaging a drive bar.

One characteristic of this positive traction permeate tube thatconstitutes an important improvement over the prior art is that thefittings provide positive traction. The intermediate section of thefitting with the opening of hexagonal or polygonal shape remains in thetube after the membrane element is exhausted, thus the positive tractionpermeate tube is re-usable, maintaining the original capability ofpositive traction. When the membrane element becomes too old, themembrane leaves can be scraped off, the stainless steel tube cleaned andthe permeate tube is then ready to be used again, just like new, to rolla new membrane element.

The number and disposition of perforations in the permeate tube is notcritical. A suitable arrangement utilizes a limited number ofperforations in four longitudinal rows to allow the passage of permeateinto the permeate tube center when the novel positive traction permeatetube is operative within a membrane element. The number of perforationsis limited to assure that the permeate tube can withstand high torqueconditions and pressure conditions in wrapping under a vacuum. Theperforations may be arranged in two sets of opposing rows for a total offour rows displaced 90 degrees from each other.

Positive traction permits the membrane elements to be wound around thenovel permeate tubes at higher winding tensions without having thepermeate tube slip. Positive traction is distinguishable from the priorart in that the interlocking means permit precise control at hightension winding without breakage as found in making spiral woundmembrane elements with prior art plastic permeate tubes or withoutslippage as found in making spiral wound membrane elements with priorart stainless steel permeate tubes not having positive tractioninterlocking. A positive traction permeate tube allows membrane elementsto be wound at sufficiently high tension without unacceptable breakageduring manufacture when compared with the slippage or breakage thatoccurs in making membrane filtration elements using prior art plasticpermeate tubes or non-interlocking stainless steel tubes, wound undersimilarly high tensions.

316L stainless steel is a most preferred sanitary stainless steel. Thismaterial provides good machining, good welding and corrosion-resistanceattributes in addition to having the ability to be polished to a mirrorfinish. Sanitary tubing made of 316L stainless steel is a standardtubing which is already polished from the factory. 316L stainless steeltubing is the standard in the industry and meets the sanitaryrequirements necessary for permeate tube applications. Accordingly, infabricating the positive traction permeate tube of the present inventionthe sanitary tubing available in the market which complies with 3ASanitary Standards is used. Sanitary end fittings, manufactured to thesame 3A Sanitary Standards are then welded to each end of the sanitarytubing. Welding is effected using automatic orbital equipment thatproduces a full penetration butt-weld with a clean bead on both theexterior and interior surface of the weld. No further grinding orpolishing is required. The resulting weld meets the requirements forsanitary systems. The tubing and sanitary fittings must be composed ofthe same stainless steel alloy in order for the penetration butt-weld toform the required clean bead on both the interior and exterior surfaceof the weld.

After both ends of the tube are welded to positive traction fixtures, an80 grid emory cloth is preferably applied to the outer surface of thetubes, on the glue zone proximate the tube ends, to roughen the surfacein order to secure good binding of the glue used to set the membraneleaves in place. As noted, after welding both fittings to the sanitarytubing, the exterior surface of the fittings plus an additional twoinches of the tubing on each end are roughed up using an emery cloth (80grid) to secure good adhesion of glue used to adhere the membrane leavesto the permeate tube. Membrane element wrapping utilizing the positivetraction permeate tube enables management and control of torque andfacilitates trim of the membrane at each of the ends of the permeatetube. Moreover, when membrane replacement is required, the positivetraction permeate tube can be re-used by removing the spirally wrappedmembrane, cleaning the permeate tube and wrapping new membrane on thepositive traction permeate tube.

The term “sanitary” when used herein to describe the tubing and fittingsmeans that the described components of the permeate tube meet the 3ASanitary Standards for sanitary applications. The term positive tractionwhich is used to characterize the permeate tube of the present inventionrelates that the architecture of the permeate tube includes means forengaging a driving bar without slippage. Of note in the presentinvention, the circumference of the fittings and the sanitary tube arethe same and after the fittings are affixed to the tube usingbutt-welding with full penetration a clean bead is produced on theinterior which does not require any polishing according to 3A SanitaryStandards.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention will become more apparent fromthe detailed description of the invention and disclosure of the bestmode in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of a prior art spiral wound membraneelement with a plastic permeate tube, before being cut to length;

FIG. 2 is an exploded view of the prior art spiral-wound membraneelement with a plastic permeate tube of FIG. 1 after being cut to finallength and the two tips removed to be discarded;

FIG. 3 is a perspective exploded view of the components of the novelpermeate tube of the invention;

FIG. 4 is a perspective view of an assembled novel permeate tubeconstructed in accordance with the preferred embodiment of theinvention;

FIG. 5 is a perspective view partly in section of a tubular end fittingfor the novel permeate tube of FIG. 4;

FIG. 6 is a perspective view of a central drive bar for imparting apositive traction for constructing a novel spiral wound membrane elementutilizing the permeate tube of the invention;

FIG. 7 is an end view of a tubular end fitting for a novel permeate tubein accordance with the invention;

FIG. 8 is a perspective view of the permeate tube of the presentinvention illustrating application of the central drive bar of FIG. 6and drive system for providing positive traction enabling production ofa tightly wound spiral wound membrane element;

FIG. 9 is an exploded perspective view of components for a positivetraction drive system for the novel permeate tube in accordance with theinvention;

FIG. 10 is a perspective view of a drive chuck and cap for a positivetraction drive system for the novel permeate tube in accordance with theinvention;

FIG. 11 is a perspective view of a support chuck and cap for a positivetraction drive system for the novel permeate tube in accordance with theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS INCLUDING BEST MODE

According to the preferred embodiment and best mode, a positive tractionpermeate tube for spiral wound membrane elements is made from sanitarystainless steel components. Positive traction is distinguishable fromthe prior art in that the interlocking means at the ends of the tubepermit precise control at high tension winding without slippage orbreakage as found in making spiral wound membrane elements with priorart plastic permeate tubes or non-positive traction stainless steeltubes. As heretofore noted in accordance with the prior art, in makingspiral wrapped membranes with stainless steel permeate tubes, expandingchucks are inserted at the ends of a perforated stainless steel tube andattached to the drive system of a rolling machine. When conventionalwinding tensions are exceeded, slippage occurs. A positive tractionpermeate tube allows membrane elements to be wound at sufficiently hightension without unacceptable breakage during manufacture when comparedwith the slippage or breakage that occurs in making filtration elementsusing prior art plastic permeate tubes or non-positive tractionstainless steel tubes, wound under similarly high tensions.

Other materials having some or all of the desirable properties ofsanitary stainless steel, such as other metals, especially austeniticand other materials that can withstand torque forces generated byproviding positive traction are known by those of ordinary skill in theart. In the most preferred embodiment the novel positive tractionpermeate tube is made from 316L sanitary stainless steel. In anotherembodiment, the novel positive traction permeate tube is made from 304sanitary stainless steel.

The novel permeate tube, according to the preferred embodiment and bestmode, is manufactured from three components as demonstrated in FIG. 3.One of the three components is a central sanitary tubing 31. The othertwo components are specially manufactured tubular end fittings 32, onefor each end 34 of the sanitary tubing 31. The fittings 32 are requiredat each end 34 of the central sanitary tubing 31 in order to provide thesealing surface to receive the interconnector-ATD with an O-ring or lapseal. Central longitudinal axes 35, 36 and 37 of the first fitting 32with a first opening 38, the tubing 31 and the second fitting 32 with asecond opening 39, respectively, are parallel and coincident. Eachfitting 32 is a positive traction device having an anti-telescopingdevice opening. One fitting 32 has the first opening 38, the otherfitting 32 has the second opening 39. When assembled together by fullpenetration butt-welding, as shown in FIG. 4, these three componentstogether constitute a novel permeate tube 45, according to the mostpreferred embodiment of the invention. The outer cross-section of thepermeate tube 45 is substantially circular because the membrane elementmust be “substantially” cylindrical in order to provide a good fitinside a pressure vessel that houses the membrane element.

In an example of the most preferred embodiment and best mode there is afinished tube length of 38.000 inches, an outer diameter of 1.50 inches,an inner diameter of 1.138 inches at the ends, having a length of theend fitting of 2.00 inches, a wall thickness in the mid-section sanitarytubing of 0.065 inches, having 29 perforations in each of four rows,with a perforation diameter of 0.125 inches, a distance between theperforations of 1.00 inches, and a hexagonal longitudinal hole ofapproximately 0.945 inches across to accept a 15/16″ hexagonal centralbar (0.9375 inches across). In an example of another embodiment there isa tube length of 38.000 inches, an outer diameter of 2.50 inches, aninner diameter of 2.250 inches, having a length of the end fitting of2.00 inches, a wall thickness in the mid-section sanitary tubing of0.065 inches, having 39 perforations in each of four rows, with aperforation diameter of 0.188 inches, a distance between theperforations of 0.75 inches, and a hexagonal longitudinal hole ofapproximately 1.908 inches across to accept a 1⅞″ hexagonal central bar(1.875 inches across). In other embodiments there is a tube length of10-60 inches, an outer diameter of 0.75-2.50 inches, an inner diameterof 0.25-2.25 inches, having a length of the end fitting of 0.5-3.00inches, a wall thickness in the mid-section sanitary tubing vessel of0.040-0.080 inches, having 15-50 perforations with a perforationdiameter of 0.10-0.25 inches, a distance between the perforations of0.50-2.50 inches, and a hexagonal longitudinal hole of approximately0.65-1.30 inches across to accept a hexagonal central bar 0.60-1.28inches across.

In the preferred embodiment and best mode, the tubular end fittings aremachined from a cylinder of sanitary stainless steel, also type 316L,and each tubular end fitting has the same outer diameter as the outerdiameter of the central sanitary tubing to which each end fitting willbe affixed. As demonstrated in FIG. 5, a finished tubular end fitting 50has a longitudinal opening 51 through a solid metal piece 52perpendicular to an outer wall 53 and a longitudinal axis 54 of thefitting 50 so that the opening si can provide longitudinal access intothe interior of a positive traction permeate tube. In the most preferredembodiment, this opening 51 is machined or cut from the solid metalpiece 52 or a hollow bar prior to joining the end fitting to the centralsanitary tubing.

The longitudinal opening 51 in the end fitting 50 provides longitudinalaccess into the interior of the positive traction permeate tube. Thisopening 51 is designed to accommodate a central bar that will functionin a positive traction drive system to provide rotational force toprovide high tension winding in applying the membrane element around thepositive traction permeate tube. In the most preferred embodiment andbest mode, the longitudinal opening 51 is shaped to form a regularhexagon in the center of the solid metal piece 52 of the tubular endfitting. The hexagonal longitudinal opening 51 will accommodate ahexagonal-shaped central bar 60 having an axial hole 61 for drawing avacuum through radial holes 62 in the positive traction drive system, asshown in FIG. 6.

In the best mode, the size of the hexagonal opening in a tubular endfitting/mating element can vary, provided engagement and rotationoccurs. However, in the preferred embodiment and best mode, thehexagonal opening will match the hexagonal size of the central bar 60 inthe positive traction drive system. The opening in the end fitting willhold the central bar 60 that passes through the hexagonal hole in theend fitting when the positive traction permeate tube is engaged by apositive traction drive system for winding the spirally wound membraneunder high tension. As will be recognized by those skilled in the art,the opening may be other than hexagonal, e.g. octagonal, etc. Therequired configuration of the opening and bar simply calls for the barto engage or interlock with the opening and thereby provide positivetraction.

In the preferred embodiment and best mode in FIG. 7, a hexagonal hole 71in an end fitting 70 is cut or machined so that a center 74 of thehexagonal hole 71 is centered in the solid portion of the end fittingand provides longitudinal access to the interior of the positivetraction permeate tube. However, the present invention also contemplatesa positive traction permeate tube having end fittings with either onehole or a plurality of holes machined or cut into each end fitting forproviding longitudinal access to the positive traction permeate tubeinterior. Any alternative hole or plurality of holes in each end fittingcan be of various shapes other than a hexagon, such as a triangle, asquare or other polygonal shape. These alternative embodiment holes canbe centered or non-centered with or about the longitudinal axis of thetubular end fitting. Almost any shape hole in the end fitting can bepracticed, provided that the hole or holes provide an edge or surfaceagainst which a rotating central bar in a positive traction drive systemcan develop a moment of force having a vector pointing perpendicular toand displaced from the longitudinal axis of the positive tractionpermeate tube when the drive system is engaged in rotating the permeatetube.

In FIG. 7, an edge 72 of the hexagonal opening 71 provides a surfaceagainst which a moment of force vector 73 is produced when a central baris rotated. The vector 73 is perpendicular to the longitudinal axisthrough the center 74 of the positive traction permeate tube to whichthe end fitting 70 is affixed.

In the preferred embodiment each tubular end fitting/mating element iswelded to an end of the central sanitary tubing component. In the mostpreferred embodiment the welding is accomplished by forming a fullpenetration butt-weld between the tubular end fitting and the centralsanitary tubing component. Butt-welds are achieved when two pieces ofmetal are positioned coplanar and touching on one edge. When the twopieces are fused at the touching edge a butt-weld is formed. Prior toforming the butt-weld, the seams or abutment sections are first cleanedand prepared, and set on orbital welding equipment followed by weldingtogether the central sanitary tubing component and a tubular endfitting. By securing full penetration welding, a smooth bead is formedon the interior surface of the tube. This smooth bead conforms with the3A Sanitary Standards and requires no further grinding or polishing.After the welding is finished, a number 80 grid emery cloth is appliedto roughen the outer surface of the tubes, on the glue zone at the ends(approximately 4″ long), to secure good binding of the glue used to setin place the membrane leaves.

Because the permeate tube will operate as part of a spirally woundmembrane element meeting closely regulated sanitary requirements, wheretubing is used having a surface roughness that does not meet thesanitary standards, the surface must be machined and polished to meetthe applicable 3A Sanitary Standards.

In the preferred embodiment, the positive traction permeate tube isfabricated using components having precise size tolerances for the finallength and inside diameter at both ends prior to starting themanufacturing process of the membrane filtration element. Asconstructed, the positive traction permeate tubes provide for hightension positive traction using a positive traction drive systemdesigned for manufacturing high tension spirally wound membranefiltration elements, while maintaining precise finished length.

The central sanitary tubing of the permeate tube is preferableperforated after welding the tubular end fittings on either end of thecentral sanitary tubing, as shown in FIG. 4. Perforations 46 provideaccess to the interior of the positive traction permeate tube. Inapplying the membrane element under high tension using a positivetraction drive system, a vacuum can be drawn through one or both of thelongitudinal openings of the positive traction permeate tube, whichopenings are otherwise sealed off to help maintain the integrity of thevacuum.

The vacuum provides a negative pressure on the membrane element duringthe positive traction high tension winding. This negative pressure helpsto better adhere and compact the membrane leaves to form a membranefiltration element. Also of note, in accordance with the presentinvention an end fitting is welded to each of the open ends of thesanitary tubing, thereby providing a sealing surface for theATD/interconnector required at both ends of the permeate tube.

FIGS. 8 and 9 demonstrate a positive traction drive system 80 forrotating a positive traction permeate tube 45 having the perforations 46during winding of the membrane element under high tension. A rollingmachine (not shown) must be fitted with the drive components to rotatethe positive traction permeate tube 45. A drive chuck 82 has an innernarrower cylindrical body 85 which abuts one end of the permeate tube45. A support chuck 83 has an identical inner narrower cylindrical body84 which abuts an opposite end of the permeate tube 45. The drive chuck82 has an axial hole 87 through which a vacuum can be applied to aninterior of the permeate tube 45. In FIG. 9, components of a positivetraction drive 90, according to the preferred embodiment, include thecentral bar 60 that is hexagonal and two chucks that can be either thedrive chuck 82 or the support chuck 83, provided that at least one ofthe chucks is a drive chuck. Each chuck in the preferred embodiment alsohas a hexagonal cap 94.

The hexagonal central bar 60 matches the longitudinal hexagonal openingin the two end fittings of the positive traction permeate tube. Thecentral bar 60 transmits the torque generated by the rolling machine toboth ends of the positive traction permeate tube. In addition, thehexagonal central bar 60 has a greater length than the positive tractionpermeate tube in which it is used to allow the central bar 60 to beengaged by one or more drive chucks 82. The central bar 60 may also haveone or more holes to allow drawing of a vacuum in the interior of thepositive traction permeate tube while engaged to the positive tractiondrive during winding of the membrane element. In the preferredembodiment, there is an axial hole in the central bar 60 adjoining thedrive chuck 82 through which the vacuum is drawn from the permeate tubethrough radial holes placed nearer the center of the hexagonal centralbar 60.

The drive chuck 82 and the support chuck 83 are also shown in FIGS. 10and 11, respectively. The drive chuck 82 and any support chuck 83connect the ends of the hexagonal central bar 60 of FIG. 9 to a rollingmachine through a bushing or a bearing. The chucks 82 and 83 each hold ahexagonal cap 99 and 94, respectively, in FIGS. 10 and 11, which cap(99, 94) is a removable part, preferably made of hard plastic material.The hexagonal cap (99, 94) has two functions: (a) centering a positivetraction permeate tube by mating a conical surface of the hexagonal cap(99, 94) with a chamfer on the positive traction permeate tube end; and(b) providing two grooves 102, one on each side, to allow O-rings toseal the interior of an engaged positive traction permeate tube andallow the application of the vacuum to the positive traction permeatetube interior during the rolling and tensioning process. The drive chuck82 is very similar to the support chuck 83 in general. However, thedrive chuck 82 also has a spline cut 103 or some equivalent structure toengage the drive of the rolling machine. Either chuck 82 or 83 may havea hole to allow the application of the vacuum into the positive tractionpermeate tube interior. In FIG. 10, an axial hole 104 for the vacuum isdemonstrated.

A membrane filtration element incorporating a positive traction permeatetube may use a positive traction drive system to spirally wind amembrane element under high tension about the positive traction permeatetube under positive traction conditions. Preferably a vacuum is appliedthrough the positive traction permeate tube from the positive tractiondrive system while spirally winding the membrane element.

OTHER EMBODIMENTS

In a further embodiment, the invention pertains to a positive tractionpermeate tube comprising (a) a sanitary tubing having a first open end,a second open end, a sanitary tubing wall defining a sanitary tubinginterior and sanitary tubing exterior, a sanitary tubing longitudinalaxis and a plurality of perforations in the sanitary tubing wallproviding access to the sanitary tubing interior; (b) a first fittinghaving a longitudinal axis, the first fitting being affixed contiguouswith the first open end of the sanitary tubing such that thelongitudinal axis of the sanitary tubing and the longitudinal axis ofthe first fitting are parallel and coincident, the first fitting havinga longitudinal opening cut through a solid portion of the first fitting,the longitudinal opening defined by at least one surface against whichan applied force produces a moment of force having a vectorperpendicular to and displaced from the longitudinal axis of thesanitary tubing and the parallel and coincident longitudinal axis of thefirst fitting when affixed contiguously with the first open end of thesanitary tubing, and (c) a second fitting having a longitudinal axis,the second fitting being affixed contiguous with the second open end ofthe sanitary tubing such that the longitudinal axis of the sanitarytubing and the longitudinal axis of the second fitting are parallel andcoincident, the second fitting having a longitudinal opening cut througha solid portion of the second fitting, the longitudinal opening definedby at least one surface against which an applied force produces a momentof force having a vector perpendicular to and displaced from thelongitudinal axis of the sanitary tubing and the parallel and coincidentlongitudinal axis of the second fitting when affixed contiguously withthe open end of the sanitary tubing.

In other embodiments the invention pertains to a tube wherein thepermeate tube is defined by an outer diameter having a circularcross-section; wherein the permeate tube comprises stainless steel;wherein the permeate tube comprises 316L stainless steel; wherein thepermeate tube components are welded together; wherein the permeate tubecomponents are welded together using full penetration butt-welding; andwherein the permeate tube has a polished surface in accordance with 3ASanitary Standards.

In another embodiment, the invention pertains to a method of making apositive traction permeate tube comprising: (a) providing (1) a sanitarytubing having a first open end, a second open end, a sanitary tubingwall defining a sanitary tubing interior and sanitary tubing exterior, aplurality of perforations in the sanitary tubing providing access to thesanitary tubing interior, and a sanitary tubing longitudinal axis; (2) afirst fitting having a longitudinal axis and a solid portion for alongitudinal opening; (b) cutting a longitudinal opening through thesolid portion of the first fitting, the longitudinal opening defined byat least one surface against which an applied force produces a moment offorce having a vector perpendicular to and displaced from thelongitudinal axis of the first fitting; (c) affixing the sanitary tubingand the first fitting to each other contiguously along the first openend of the sanitary tubing such that the longitudinal axis of thesanitary tubing and the longitudinal axis of the first fitting areparallel and coincident; (d) providing a second fitting having alongitudinal axis and a solid portion for a longitudinal opening; (e)cutting a longitudinal opening through the solid portion of the secondfitting, the longitudinal opening defined by at least one surfaceagainst which an applied force produces a moment of force having avector perpendicular to and displaced from the longitudinal axis of thesecond fitting; and (f) affixing the sanitary tubing with the secondfitting to each other contiguously along the second open end of thesanitary tubing such that the longitudinal axis of the sanitary tubingand the longitudinal axis of the second fitting are parallel andcoincident to form a positive traction permeate tube. In otherembodiments, the invention pertains to a method of making a positivetraction permeate tube wherein the affixing is accomplished by welding;wherein the affixing is accomplished by full penetration butt-welding;and further comprising polishing the positive traction permeate tubewhen needed to comply with 3A Sanitary Standards.

In another embodiment the invention pertains to a permeate tube devicefor spirally wrapped membrane elements comprising a) a hollow tubularelement having an inside wall and an outside wall and a first end and asecond end; b) a first positive traction device affixed to said firstend; (c) a second positive traction device affixed to said second end;and d) a plurality of holes connecting said inside wall with saidoutside wall. The hollow tubular element is preferably a stainless steelsubstantially cylindrical element to which the positive tractiondevices, also made of stainless steel, are welded, most preferably byfull penetration welding utilizing orbital welding equipment.

In another embodiment the invention pertains to a substrate apparatusfor a spirally wrapped membrane element comprising a) a positivetraction torque device having a means for positive engagement toprecisely control the rotational position and amount of torques impartedto said positive traction torque device; b) a permeate tube having bothends permanently attached to each of a pair of said positive tractiontorque devices; and c) a plurality of holes in said permeate tube whichin conjunction with the composition of said permeate tube has a torquecapacity equal to or greater than the torque of said positive tractiontorque device.

In another embodiment the invention pertains to a permeate tube devicehaving first and second open ends and having holes therein for use as asubstrate of a spirally wrapped membrane element wherein the improvementcomprises first and second positive traction torque devices welded tosaid first and second open ends of the permeate tube having a matingmechanism to precisely control the rotational position and torqueimparted to the tube.

In still another embodiment, the invention pertains to a positivetraction, permeate tube comprising: (a) a sanitary tubing having a firstopen end, a second open end, a sanitary tubing wall defining a sanitarytubing interior and substantially circular sanitary tubing exterior, asanitary tubing longitudinal axis and a plurality of perforations insaid sanitary tubing wall providing access to said sanitary tubinginterior; (b) a first fitting having a longitudinal axis, said firstfitting being affixed contiguous to said first open end of said sanitarytubing such that said longitudinal axis of said sanitary tubing and saidlongitudinal axis of said first fitting are parallel and coincident,said first fitting having a longitudinal opening cut through a solidportion of said first fitting, said longitudinal opening being definedby at least one surface against which an applied force produces a momentof force having a vector substantially perpendicular to and displacedfrom said longitudinal axis of said sanitary tubing and said paralleland coincident longitudinal axis of said first fitting when affixedcontiguously to said first open end of said sanitary tubing; and (c) asecond fitting having a longitudinal axis, said second fitting beingaffixed contiguous to said second open end of said sanitary tubing suchthat said longitudinal axis of said sanitary tubing and saidlongitudinal axis of said second fitting are parallel and coincident,said second fitting having a longitudinal opening cut through a solidportion of said second fitting, said longitudinal opening being definedby at least one surface against which an applied force produces a momentof force having a vector substantially perpendicular to and displacedfrom said longitudinal axis of said sanitary tubing and said paralleland coincident longitudinal axis of said second fitting when affixedcontiguous to said second open end of said sanitary tubing.

In still yet other embodiments, the invention pertains to a permeatetube of wherein said permeate tube is defined by an outer diameterhaving a substantially circular cross-section; wherein said permeatetube comprises stainless steel; wherein said permeate tube comprises316L stainless steel; wherein said first and second fittings are affixedto said sanitary tubing by full penetration butt welding; wherein saidpermeate tube has a polished surface as required by 3A SanitaryStandards for sanitary applications; wherein said first and secondfittings are affixed to said sanitary tubing by full penetrationautomatic orbital welding and said permeate tube has a polished surfaceas required by 3A Sanitary Standards for sanitary applications; whereinsaid plurality of perforations in said sanitary tubing wall are arrangedat diametrically opposing loci of the sanitary tubing wall; or whereinthe perforations are arranged in at least four rows runninglongitudinally along a substantial portion of the length of the sanitarytubing wall.

In yet still other embodiments, the invention pertains to a method ofmaking a stainless steel positive traction permeate tube comprising: (a)utilizing a stainless steel sanitary tube having a polished surface asrequired by 3A Sanitary Standards for sanitary applications and having afirst open end, a second open end, a sanitary tubing wall defining asanitary tubing interior and a sanitary tubing exterior, a plurality ofperforations in said sanitary tubing wall providing access to saidsanitary tubing interior, and a sanitary tubing longitudinal axis; (b)employing a first fitting having a polygonal opening with a longitudinalaxis and a solid portion for a longitudinal opening having a polishedsurface as required by 3A Sanitary Standards for sanitary applications;(c) employing a second fitting having a polygonal opening with alongitudinal axis and a solid portion for a longitudinal opening havinga polished surface as required by 3A Sanitary Standards for sanitaryapplications; (d) welding said first open end of said sanitary tubingand said first fitting to each other contiguously along said first openend of said sanitary tubing such that said longitudinal axis of saidsanitary tubing and said longitudinal axis of said first fitting areparallel and coincident; and (e) welding said second open end of saidsanitary tubing and said second fitting to each other contiguously alongsaid second open end of said sanitary tubing such that said longitudinalaxis of said sanitary tubing and said longitudinal axis of said secondfitting are parallel and coincident to form said positive tractionpermeate tube; or also wherein the welding is accomplished by fullpenetration butt-welding; or wherein said first and said second fittingsare welded to said sanitary tubing by full penetration automatic orbitalwelding.

In another embodiment, the invention pertains to a positive tractionpermeate tube for spirally wrapped membrane elements comprising: (a) asubstantially cylindrical hollow tubular element having an inside wall,a cylindrical outside wall, a first open end and a second open end; (b)a first positive traction device affixed to said first open end, (c) asecond positive traction device affixed to said second open end; and (d)a plurality of holes connecting said inside wall with said outside wall.

In yet another embodiment, the invention pertains to a positive tractionpermeate tube wherein said substantially cylindrical hollow tubularelement is a sanitary stainless steel element and first and secondpositive traction devices are composed of sanitary stainless steelmeeting the 3A Sanitary Standards for sanitary applications and saidfirst and second positive traction devices are affixed to said first andsecond open ends respectively by a full penetration butt-weld.

In yet another embodiment, the invention pertains to a cylindricalsanitary fitting for affixation at an open end of a sanitary perforatedcylindrical tube adapted to accept an anti-telescoping device and engagea drive bar comprising: (a) a substantially cylindrical sanitary fittinghaving an interior end having a face defined by a plane perpendicular tothe axis of the fitting and an opening coaxial with the fitting; (b) anexterior end having a face defined by a plane perpendicular to the axisof the fitting and a cylindrical opening, coaxial with the fittingproviding a cylindrical inner surface adapted to accept ananti-telescoping device with a sealing device; and (c) an intermediatesection between said interior and exterior ends having a polygonalopening coaxial with the fitting adapted to engage a drive bar toachieve positive traction.

And in yet other embodiments, the invention pertains to a cylindricalsanitary fitting wherein said cylindrical sanitary fitting is comprisedof stainless steel meeting the requirements of 3A Sanitary Standards forsanitary applications; wherein the cylindrical sanitary fitting is amachined solid block; wherein the stainless steel fitting is composed of316L stainless steel; wherein the stainless steel fitting is composed of304 stainless steel or wherein said polygonal opening is hexagonal.

In yet another embodiment, the invention pertains to a permeate tubedevice for spirally wrapped membrane elements comprising: a) a hollowsubstantially cylindrical stainless steel tubular element having aninside wall and an outside wall and a first end and a second end; b) afirst positive traction device having an anti-telescoping device openingdisposed at or near one end and a polygonal: shaped mating openingdisposed at or near the other end, said first positive traction deviceaffixed to said first end of said hollow tubular member; c) a secondpositive traction device having an anti-telescoping device openingdisposed at or near one end and a polygonal-shaped mating openingdisposed at or near the other end, said second positive traction deviceaffixed to said second end of said hollow tubular member; and d) aplurality of holes connecting said inside wall with said outside wall ofsaid substantially cylindrical sanitary stainless steel hollow tubularelement; or wherein the anti-telescoping device openings are cylindricalopenings; or wherein said first and second traction devices are affixedto said sanitary stainless steel substantially cylindrical tubularelements by a full penetration butt-weld.

In yet another embodiment, the invention pertains to a positive tractionpermeate tube over which a spirally wrapped membrane element may beformed comprising: a) a first positive traction torque device having ameans for positive engagement to precisely control the rotationalposition and amount of torques imparted to said positive traction torquedevice; b) a second positive traction torque device having means forpositive engagement to precisely control the rotational position andamount of torque imparted to said positive traction torque device; c) apermeate tube having a first end permanently attached to said firstpositive traction torque device and a second end permanently attached tosaid second positive traction torque device; and d) a plurality of holesin said permeate tube which in conjunction with the chemical compositionof said permeate tube has a torque capacity equal to or greater than thetorque of said positive traction torque device.

It will be recognized the invention is capable of numerous changes andmodifications by those skilled in the art. These and such othervariations are intended to be included in the scope of the appendedclaims. As used herein and in the following claims, the word ‘tube’ isnot limited according to its technical sense to mean a perfectcylindrical passage defined by a circular cross-section. The outercross-section, however, must be substantially circular because themembrane element must be “substantially” cylindrical in order to providea good fit inside the pressure vessel in which the membrane element ishoused during use.

As used herein and in the following claims, the word ‘comprising’ or‘comprises’ is used in its technical sense to mean the enumeratedelements include but do not exclude additional elements which may or maynot be specifically included in the dependent claims. It will beunderstood that such additions, whether or not included in the dependentclaims, are modifications which can be made within the scope of theinvention. It will be appreciated by those skilled in the art that awide range of changes and modifications can be made to the inventionwithout departing from the spirit and scope of the invention as definedin the following claims.

CHART OF ELEMENTS Number Description 10 prior art spiral-wound membranefiltration element 11 prior art plastic permeate tube 12 membraneelement 15 notch in prior art plastic permeate tube 31 central stainlesssteel sanitary tubing 32 stainless steel sanitary end fitting/matingelement 34 sanitary tubing end 38 first device opening for ATD 39 seconddevice opening for ATD 45 novel permeate tube according to inventionbest mode 46 perforation in permeate tube 50 finished tubular endfitting/mating element 51 longitudinal opening 52 solid metal piece 53outer wall 54 fitting longitudinal axis 60 central bar 61 central baraxial hole 62 central bar radial hole 70 end fitting with hexagonalopening/hole 71 hexagonal opening/hole 72 edge of hexagonal opening/hole73 moment of force vector 74 longitudinal axis through center ofpermeate tube 80 drive system and permeate tube 81 permeate tube ondrive system 82 drive chuck 83 support chuck 84 outer cylindrical bodyof the drive chuck 85 outer cylindrical body of the support chuck 87axial hole for vacuum connection 90 drive system 94 hexagonal cap 99hexagonal cap 102 groove for O-ring 103 spline cut 104 chuck axial holefor vacuum connection

What is claimed is:
 1. A permeate tube with a spirally wrapped membranecomprising: (a) a positive traction stainless steel hollow tube having afirst open end, a second open end, an inside wall and substantiallycircular stainless steel tube exterior with a longitudinal axis having aplurality of perforations in said positive traction stainless steelhollow tube to provide a direct communication between the inside walland the substantially circular stainless steel tube exterior; (b) afirst positive traction fitting having a longitudinal axis and alongitudinal opening with an anti-telescoping device opening to preventtelescoping and a polygonal-shaped opening disposed within saidlongitudinal opening with the polygonal-shaped opening having a crosssection being defined by at least one internal side surface of the firstpositive traction fitting, said first positive traction fitting beingaffixed contiguous, parallel and coincident to said first open end ofsaid positive traction stainless steel hollow tube; (c) a secondpositive traction fitting having a longitudinal axis and a longitudinalopening with an anti-telescoping device opening to prevent telescopingand a polygonal-shaped opening disposed within said longitudinal openingwith the polygonal-shaped opening having a cross section being definedby at least one internal surface of the second positive tractionfitting, said second positive traction fitting being affixed contiguous,parallel and coincident to said second open end of said positivetraction stainless steel hollow tube; (d) an inner central bar having apolygonal-shaped cross section with an axial hole therethrough andradial holes connected to the axial hole in the inner central bar fordrawing a vacuum through radial holes therein said inner central barhaving a polygonal-shaped cross section to mate with thepolygonal-shaped opening in the first positive traction fitting and thesecond positive traction fitting; and (e) the spirally wrapped membrane,wrapped around the positive traction stainless steel hollow tube with atorque or tightness controlled by the first positive traction fitting,the second positive traction fitting and the inner central bar whereinsaid spirally wrapped membrane element is prevented from telescoping bythe first and second positive traction fitting having theanti-telescoping device opening.
 2. The permeate tube of claim 1 whereinsaid polygonal-shaped cross-section of the inner central bar ishexagonal.
 3. The permeate tube of claim 1 wherein said positivetraction stainless steel hollow tube comprises 316L stainless steel. 4.The permeate tube of claim 3 wherein said first and second positivetraction fittings are affixed to said positive traction stainless steelhollow tube by full penetration automatic orbital welding and saidpermeate positive traction stainless steel hollow tube has a polishedsurface.
 5. The permeate tube of claim 4 wherein the plurality ofperforations are arranged in at least four rows running longitudinallyalong a substantial portion of the length of the positive tractionstainless steel hollow tube.
 6. The permeate tube of claim 1 whereinsaid positive traction stainless steel hollow tube comprises 304stainless steel.
 7. The permeate tube of claim 1 wherein said first andsecond positive traction fittings are affixed to said positive tractionstainless steel hollow tube by full penetration butt welding.
 8. Thepermeate tube of claim 1 wherein said positive traction stainless steelhollow tube has a polished surface.
 9. The permeate tube of claim 1wherein said plurality of perforations in said positive tractionstainless steel hollow tube are arranged at diametrically opposing locithe positive traction stainless steel hollow tube.
 10. A method ofmaking a permeate tube with a wrapped membrane as in claim 1 comprising:(a) utilizing the positive traction stainless steel hollow tube having apolished surface; (b) employing the first positive traction fitting withthe longitudinal axis and with the longitudinal opening's solid portionhaving a polished surface and with the polygonal-shaped opening having anontapered, mating cross section defined by at least one internal sidesurface against which an applied force produces a moment of force havinga vector substantially perpendicular to and displaced from saidlongitudinal axis of the first positive traction fitting; (c) employingthe second positive traction fitting with the longitudinal axis with thelongitudinal opening's solid portion having a polished surface and withthe polygonal-shaped opening having a nontapered, mating cross sectiondefined by at least one internal side surface against which an appliedforce produces a moment of force having a vector substantiallyperpendicular to and displaced from said longitudinal axis of the secondpositive traction fitting; (d) welding said first open end of saidpositive traction stainless steel hollow tube and said first positivetraction fitting to each other contiguously along said first open end ofsaid positive traction stainless steel hollow tube such that thelongitudinal axis of said positive traction stainless steel hollow tubeand said longitudinal axis of said first positive traction fitting areparallel and coincident; (e) welding said second open end of saidpositive traction stainless steel hollow tube and said second positivetraction fitting to each other contiguously along said second open endof said positive traction stainless steel hollow tube such that thelongitudinal axis of said positive traction stainless steel hollow tubeand said longitudinal axis of said second positive traction fitting areparallel and coincident to form said permeate tube; (f) accommodatingthe inner central bar by the permeate tube's longitudinal opening of thefirst positive traction fitting and the longitudinal opening of thesecond positive traction fitting, said inner central bar having apolygonal-shaped cross section to mate with the polygonal-shaped openingin the first positive traction fitting and the polygonal-shaped openingin the second positive traction fitting, the inner central bar with theaxial hole therethrough for drawing a vacuum through radial holestherein; and (g) drawing vacuum through the axial hole of the innercentral bar, through the radial holes of the inner central bar, andthrough the permeate tube and, spirally winding a membrane elementaround the permeate tube to form the permeate tube with the wrappedmembrane.
 11. The method of making according to claim 10 wherein thewelding is accomplished by full penetration butt-welding.
 12. The methodof making according to claim 10 wherein said first positive tractionfitting and said second positive traction fitting are welded to saidpositive traction stainless steel hollow tube by full penetrationautomatic orbital welding.
 13. The method of making according to claim10 wherein the polygonal-shaped cross section of the inner central barand the polygonal-shaped opening of the first positive traction fittingand the polygonal-shaped opening of the second positive traction fittingare hexagonal.
 14. A positive traction permeate tube for spirallywrapped membrane element comprising: (a) a substantially cylindricalhollow tubular element having an inside wall, a cylindrical outsidewall, a first open end and a second open end; (b) a first positivetraction device having a longitudinal opening with an anti-telescopingdevice opening to prevent telescoping of the spirally wrapped membraneelement and a polygonal-shaped opening disposed in or near thelongitudinal opening said first positive traction device affixed to saidfirst open end of the substantially cylindrical hollow tubular element;(c) a second positive traction device having a longitudinal opening withan anti-telescoping device opening to prevent telescoping of thespirally wrapped membrane element and a polygonal-shaped openingdisposed in or near the longitudinal opening said second positivetraction device affixed to said second open end of the substantiallycylindrical hollow tubular element: (d) a plurality of holes through thesubstantially cylindrical hollow tubular element connecting said insidewall with said cylindrical outside wall of the substantially cylindricalhollow tubular element; (e) an inner central bar being accommodated bythe longitudinal opening in each of the first and second positivetraction device and the inner central bar having a polygonal-shapedcross section to mate with the first positive traction device'spolygonal-shaped opening and the second positive traction device'spolygonal-shaped opening, the inner central bar having an axial hole andradial holes therethrough to connect the axial hole with the radialholes to draw a vacuum through the radial holes therein; and (f) whereinthe spirally wrapped membrane element has its torque or tightness aroundthe substantially cylindrical hollow tubular element controlled by thetension on the first positive traction device, the second positivetraction device and the inner central bar and its anti-telescopingcontrolled by the first and second positive traction fitting having theanti-telescoping device opening.
 15. The positive traction permeate tubeof claim 14 wherein said substantially cylindrical hollow tubularelement is a stainless steel element, said first and second positivetraction device are composed of stainless steel and said first andsecond positive traction device are affixed to said first open end andsaid second open end of the substantially cylindrical hollow tubularelement by a full penetration butt-weld.
 16. The positive tractionpermeate tube of claim 14 wherein the polygonal-shaped cross section ofthe inner central bar is hexagonal.
 17. A positive traction permeatetube, over which a spirally wrapped membrane element is formed,comprising: (a) a first positive traction torque device having alongitudinal opening with an anti-telescoping device opening to preventtelescoping and a polygonal-shaped opening disposed at or near one endof the longitudinal opening, the polygonal-shaped opening having a crosssection defined by at least one internal side surface of the firstpositive traction torque device to provide for a precise control of therotational position and amount of torque imparted to said first positivetraction torque device; (b) a second positive traction torque devicehaving a longitudinal opening with an anti-telescoping device opening toprevent telescoping and a polygonal-shaped opening disposed at or nearone end of the longitudinal opening, the polygonal-shaped opening havinga cross section defined by at least one internal side surface of thesecond positive traction torque device to provide for a precise controlof the rotational position and amount of torque imparted to said secondpositive traction torque device; (c) a tubular element having a hollowinterior and an exterior winding surface and a first end attached tosaid first positive traction torque device and a second end attached tosaid second positive traction torque device; (d) a plurality of holes inthe exterior winding surface of said tubular element with a directcommunication to the hollow interior and the spirally wrapped membraneelement on the exterior winding surface of said tubular element; and (e)an inner central bar having a polygonal-shaped cross section to matewith the polygonal-shaped opening in the first positive traction torquedevice and the polygonal-shaped opening in the second positive tractiontorque device said inner central bar having an axial hole and radialholes therethrough for drawing a vacuum through radial holes therein;wherein the torque or tightness of the spirally wrapped membrane elementaround the tubular element is controlled by the inner central bar and bythe first positive traction torque device and the second positivetraction torque device and its anti-telescoping controlled by theanti-telescoping device opening of the first and second positivetraction torque device.
 18. The positive traction permeate tube of claim17 wherein said first positive traction torque device and said secondpositive traction torque device are affixed to said tubular element byfull penetration butt welding.
 19. The positive traction permeate tubeof claim 18 wherein said first positive traction torque device'spolygonal-shaped opening is hexagonal and said second positive tractiontorque device's polygonal-shaped opening is hexagonal.
 20. The positivetraction permeate tube of claim 19 wherein the cross section of theinner central bar is hexagonal.
 21. The positive traction permeate tubeof claim 17 wherein the polygonal-shaped cross section of the innercentral bar and the polygonal-shaped opening in the first positivetraction torque device and the polygonal-shaped opening in the secondpositive traction torque device are hexagonal.